The invention relates to a novel pigment form of Pigment Violet 23, having a higher colour strength and higher colour saturation as well as excellent other applications properties. The pigment of the invention is obtained by kneading an amorphized form with an inorganic salt in the presence of an organic liquid and may be used in particular in printing inks. By using the same procedure, it is also possible to improve the applications properties of other pigments, amongst them in particular Pigment Red 254.
Shade, colour strength, gloss and transparency are the most important colouristic properties in printing inks and colour filters. The shade must correspond to very specific values but with maximum possible colour saturation with a view to a broad colour palette in multicolour printing. To this end, the colour strength, gloss and transparency should be as high as possible.
Additionally, pigments should nowadays be able to be used without losses in their applications properties even in modern, environmentally friendly systems, for example in water-based coating compositions or printing inks. These are formulations whose volatile fraction consists of from 5 to 100% by weight, preferably of at least 20% by weight, with particular preference of at least 50% by weight, of water, based on the overall weight of all volatile components.
C.I. Pigment Violet 23 [51319, xe2x80x9cCarbazole Violetxe2x80x9d] is an important commercial pigment which is available in many grades, for example as Cromophtal(copyright) Violet GT (Ciba Spezialitxc3xa4ten-chemie AG), Hostaperm(copyright) Violet RL Special (Clariant) or Fastogen(copyright) Super Violet RN (Dainippon Ink). However, it has been found that none of the products known to date is capable of giving complete satisfaction, especially as regards colour strength, colour saturation, gloss and transparency in the case of printing ink applications.
C.I. Pigment Red 254 [56110], the first and most important commercial 1,4-diketopyrrolo-[3,4c]-pyrrole pigment, is also available in many different grades such as for example Irgazin(copyright) Red BO or Irgaphor(copyright) Red B-CF (Ciba Specialty Chemicals Inc.). However, their coloristic properties, especially the hue and transparency, have proven still not to reach perfectly the desired values.
U.S. Pat. No. 5,281,268 discloses a process for the manufacture of xcex2-form copper phthalocyanine, wherein the crude is first dry-milled with an attriter under unknown speed conditions, then wet-milled with a kneader in the presence of an inorganic salt and an organic solvent. This pigment has excellent gloss and clearness in colours inks, coatings and coloured plastic articles.
U.S. Pat. No. 3,598,625 discloses a pigment preparation process, directed primarily also to copper phthalocyanine, in which the crude pigments are first subjected to forces of wear and shear, then treated with micropulverized salt and a solvent in a mixer. In one example, after grinding, Pigment Violet 23 is treated with 9 times the amount of salt and 1.1 times the amount of hexylene glycol. The proportion of hexylene glycol to the crystalline inorganic salt is 1 ml: 7.54 g, that of hexylene glycol to salt plus pigment is 1 ml: 8.38 g.
However, it later became evident, from a variety of sources, that the destruction of the crystallinity in the case of dioxazine pigments is disadvantageous and to be avoided.
Thus U.S. Pat. No. 4,253,839 discloses that coarse-particled dioxazine pigments should be ground in such a way that their crystal structure is essentially retained. Since this grinding process leads to defective surfaces, it absolutely must be supplemented, moreover, by aftertreatment with a solvent, which always takes place in the presence of an acid, a base or a resin.
Better results are obtained in accordance with U.S. Pat. No. 5,800,607 if crude Pigment Violet 23 is ground at high peripheral speed in a nonflocculating liquid medium, especially glycols and their ethers.
U.S. Pat. No. 4,804,417 describes the treatment of crude dioxazine violet with sulfuric acid, followed by treatment in an aqueous medium comprising a dissolved inorganic salt and small amounts of an alcohol, which gives pigments having a very high specific surface area. Crystal growth is not intended to take place.
EP 069 895 discloses the conditioning of crude polycyclic pigments, including Pigment Violet 23, by grinding with sodium sulfate, sodium chloride or aluminium sulfate in the presence of a glycol and an alkaline earth metal halide. This is intended to achieve improved transparency, a cleaner hue and a greater colour strength.
Similar advantages are achieved, however, in accordance with EP 075 182 in the conditioning of an organic pigment by treatment with polyphosphoric acid, Pigment Violet 23 again being mentioned.
According to DE 1 225 598, after dry grinding, dioxazine violet is ground further with aliphatic, araliphatic or aromatic nitro compounds, for example with nitrobenzene. However, there are no inorganic salts present.
U.S. Pat. No. 5,194,088, on the other hand, describes a process for conditioning pigments wherein the crude products are first of all preground, then simply contacted with a highly polar solvent at a temperature below 50xc2x0 C. Pigment Blue 60 and Pigment Violet 37 produce colour strengths and colour saturations which correspond approximately to those of existing products. Pigment Violet 23 is not mentioned, Pigment Red 254 only as the minor component of a solid solution into Pigment Red 202.
U.S. Pat. No. 4,785,999 describes an analogous process wherein a very specific grinding mechanism is used and the aftertreatment takes place in a very large amount of solvent. Disclosed among many other solvents are ketones, esters and dimethylformamide. Pigment Violet 23 of purportedly excellent colour strength and dispersibility is said to be obtainable in this way if the aftertreatment takes place in a xylene/water emulsion.
U.S. Pat. No. 5,626,662 and JP 09/165528 disclose processes in which pigments are first dry-ground and then ground in aqueous suspension in a powerful, high-speed ball mill.
EP 780 446 discloses the single-stage conversion of crude dioxazine violet into a strongly coloured, pure pigmentary form by means of salt grinding with 2-ethylcaproic acid.
U.S. Pat. No. 4,317,908 discloses a process for preparing the xcex2 crystal form of Pigment Violet 23 in a two-phase mixture of water and an aromatic compound.
U.S. Pat. No. 5,476,949 discloses finely divided highly transparent diketopyrrolopyrrole pigments of high chroma (CIELAB C*) and outstanding transparency. These pigments are obtained directly from the reaction of succinates with nitrites in a molar ratio of 1:2.
All of these extremely diverse methods, however, have still been unable fully to unlock the hitherto unsuspectedly high colouristic potential of pigments such as particularly Pigment Violet 23 and Pigment Red 254.
It has now been found, completely unexpectedly, that a violet pigment having improved colouristic properties and surprisingly higher colour strength may indeed be obtained by grinding amorphized Pigment Violet 23 with an inorganic salt in the presence of an organic liquid if the organic liquid used contains oxo groups and the ratio of Pigment Violet 23 and inorganic salt to the organic liquid, and the temperature, are chosen so as to give a kneadable composition.
A pigment having hitherto unattained colouristic properties is obtained which is ideally suited to all applications, especially for printing inks, preferably for water-based printing inks.